4/16/2012 4:37 PM PDT

Johnny Depp is being sued by a 52-year-old disabled woman who says she was roughed up and humiliated by the actor's bodyguards during a concert back in December ... claiming Depp's hired muscle beat her up and tore her pants off.

According to the lawsuit, filed in L.A. County Superior Court, the woman -- who identifies herself as Jane Doe -- claims she was trying to get to her seat in the V.I.P. area of an Iggy Pop concert when Depp's goons went berserk.

In her suit, Doe -- who claims she's a professor of medicine at UC Irvine -- claims for no reason, Depp's team grabbed her from behind and bear-hugged her, while restraining both of her wrists.

Doe claims the bodyguards went after her cell phone -- which contained highly sensitive confidential medical information about her patients -- and ripped it from her hand "one finger at a time."

Doe claims a member of Depp's squad eventually put her in handcuffs -- and then dragged her on the ground, causing her pants to be removed from her body, "exposing her buttocks to the other Hollywood Palladium Theater patrons.

Doe claims she suffered severe injuries in the incident -- including a dislocated left elbow, bleeding, swelling, bruising and possibly broken bones.

The woman also claims the incident caused more damage to her pre-existing spondyloarthritis and fibromyalgia -- which affects her joints and back.

Doe is suing for unspecified damages.

TMZ broke the story ... the woman had filed a report with the L.A.P.D. immediately following the incident ... and identified herself as Robin Eckert. Law enforcement sources tell us Eckert appeared intoxicated at the time she made the report.

We're told the case is still under investigation -- but law enforcement sources tell us the alleged victim has been less than cooperative.